A novel carbon dioxide- (CO2-) emulsified viscoelastic surfactant (VES) fluid system has recently been used to improve the Olmos production in the Caterina SW field in Texas. The reservoir is characterized by thin streaks of pay with potential water production in close proximity. Due to the low permeability and formation rock properties, CO2-type fracture fluids have proven to be more effective. VES-CO2 was selected as the fracturing fluid because of its higher retained proppant pack permeability and controllable rheological behavior. These unique fluid characteristics resulted in a high-conductivity fracture and a geometry that stayed out of the water-bearing zones. The outcome from 11 treatments resulted in an average production of > 430 Mscf/D and 82 BOPD in zones that were previously bypassed. The successful field applications of this new fluid system highlight the versatility of VES surfactant fluids in terms of rheological property and adaptability. Specific performance requirements can be met through modifying the functionalities of the surfactants, namely, utilizing surfactants with different functions to emulsify super-critical CO2 and still maintain all of the attributes normally associated with VES systems. VES fracturing fluid systems exhibit lower friction pressure, superior proppant transport, higher fracture conductivity and longer effective fracture half-length than conventional systems by completely eliminating polymer. Coupling the benefits of polymer-free VES fluid with a CO2-emulsified system further enhances cleanup of depleted reservoirs, extends the application to water-sensitive formations, and maintains reservoir gas saturation to prevent any potential water blocks.

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